Just east of the San Francisco Bay Area are the Berkeley Hills Walls–remnants of a massive, stone wall that stretches a distance of over fifty miles. The wall segments are up to six feet high in some places and are constructed of tightly fit limestone boulders. Scott is in intrigued by the fact that nobody knows who built the wall or even what purpose it serves. The only historical precedent for a miles-long, manmade, ancient wall is the Great Wall of China.